The invention relates to a local area radiotelephone transmission switch. The preferred embodiment utilizes pulsed radio frequency transmission schemes, such as time division multiple access transmissions (TDMA) to activate a switch or a plurality of switches. The embodiment will be permanently installed in a vehicle such as a car or a boat and interfaced to the vehicles' stereo radio, may be battery operated for portability or operated from 110 or 220 volts alternating current, to provide for a notification means of the radiotelephone transmission.
Digital Cellular Communications and Extended Specialized Mobile Radio systems use Time Division Multiple Access (TDMA) technology as a method of transmitting and receiving voice and data transmissions. This technology is currently used in the U.S. and other countries and allows multiple users to share the same voice and data channels. Each user transmits digitally encoded information in a time slot which is part of a larger frame. The modulation method is Differentially Encoded Quadrature Phase Shift Keying (DQPSK). The result of this type of radio transmission is a square root cosine transmit pulse shape. Each radiotelephone then transmits in a sequence such as follows: transmit, receive, idle. During idle time, another radiotelephone may transmit while another may receive. This process continues, thus creating a time frame. It is therefore not necessary to demodulate the DQPSK encoded in the carrier signal to utilize the transmission. The receiver used detects the electromagnetic radio frequency (rf) pulses emitted from the local area TDMA radiotelephone. The signal is then amplified. The received signal is further pulse shaped and injected into frequency detection circuitry. If the rf pulse signal is in the targeted time slot frequency, the said switch becomes active.